Abstract: Objective To investigate the predictive value of the C-reactive protein/prealbumin ratio (CPR) for spontaneous bacterial peritonitis (SBP) in patients with cirrhotic ascites. Methods This retrospective study collected demographic and clinical data from 280 patients with cirrhotic ascites who were admitted to the Affiliated Hospital of Xuzhou Medical University between January 2017 and February 2023. All patients underwent abdominal puncture, routine ascitic fluid analysis, biochemical tests, and culture examinations. The patients were divided into the SBP group (n=140) and the non-SBP group (n=140). Univariate logistic regression, LASSO regression, and multivariate stepwise logistic regression were used for variable selection and construction of a prediction model. The accuracy and consistency of the prediction model were evaluated using ROC curves, calibration curves, and decision curve analysis. Results Univariate logistic regression with a significance level of P<0.05 identified factors including the albumin-globulin ratio, international normalized ratio, CPR, white blood cell count, neutrophil percentage, lymphocyte percentage, red blood cell distribution width, serum creatinine, Child-Pugh score, and prothrombin time, which were then included in the LASSO regression. The LASSO and multivariate stepwise logistic regression analysis revealed that the international normalized ratio (OR=0.55, 95%CI:0.32-0.94), CPR (OR=67.71,95%CI:25.71-212.00), neutrophil percentage (OR=1.05,95%CI:1.02-1.08), and red blood cell distribution width (OR=1.12,95%CI:1.00-1.26) were independent risk factors for SBP in cirrhotic ascites patients. A nomogram model was constructed to predict the occurrence of SBP in these patients. The AUC of the nomogram model was 0.920 (95%CI:0.88-0.951), and after 1,000 resampling validations, the AUC became 0.919 (95%CI:0.887-0.946). The calibration curves and decision curve analysis indicated that the nomogram model had good accuracy and consistency. Conclusions CPR has good predictive value for SBP in cirrhotic ascites patients. The CPR-based nomogram model can effectively predict the occurrence of SBP.